This invention relates to a nozzle assembly, and particularly, to one which atomizes a liquid lubricant into an air stream particularly useful for coating mold cavities with a lubricant film.
The molds and dies used in casting operations require a very thin uniformly distributed coating of a liquid release agent on the forming surfaces to enable the workpieces to be easily removed from the machine at the completion of the forming operation. Numerous designs presently exist for nozzle devices which are designed to atomize release agents in air. Several of such devices are encompassed by U.S. Pat. Nos. 4,365,754 and 4,567,912 which are assigned to the assignee of this application and which are hereby incorporated by reference. Designers of such nozzles are constantly striving to improve their performance and compactness. One problem associated with some prior art nozzle devices is the presence of "slug fog" coating problems wherein an uneven ratio of liquid is mixed with air during the spray cycle or liquid drops fall from the nozzle outlet. This problem is largely attributable to the fact that nozzles are typically supplied with liquid under constant pressure, whereas a blow or atomizing air signal is intermittently applied. Variations in the blow air flow at the beginning and end of the operating cycle in conjunction with the fixed pressure of liquid results in a varying atomized liquid concentration. Such problems are also attributable to the presence of liquid trap areas within the nozzle which cause excessive amounts of liquid to be discharged at the beginning of the spray cycle. Such inconsistent liquid concentration conditions can result in excessive amounts of lubricant being applied at localized portions of the die cavity, thus causing uneven "spot" cooling of the die cavity and waste of lubricant material.
Another desirable feature for an atomizing nozzle is the ability to precisely control the flow of liquid atomized within the air stream and to provide finely atomized and uniformly dispersed droplets. These features are desirable to optimize consumption of the liquid release agent and to provide uniform coating of the forming apparatus surfaces. Another design objective is to minimize the number of moving parts within the atomizing nozzle to increase system reliability and minimize fabrication costs. It is further desirable to simplify the machining steps necessary to produce an atomizing nozzle as another step toward reducing component costs.
The above-mentioned U.S. patents assigned to the assignee of this invention largely address the above-mentioned shortcomings of prior art atomizing spray nozzles. However, it is desirable to provide additional refinements for such devices, and particularly, to improve their performance at low liquid flow rates and their ability to provide precise liquid flow adjustment. It was further desired to minimize the overall size of the spray nozzle. The present invention provides the above-mentioned desirable features. The nozzle of this invention is small and compact, making it easy to install, and is capable of a broad range of liquid flow rates while providing fine droplet size even at extremely low liquid flow rates. The nozzle is further self cleaning and dripless since the nozzle is completely cleared of liquid when it is at rest. Novel means are provided for enabling precise flow control changes through the use of an elliptically shaped flow control orifice. Very thorough atomization of the liquid is achieved through the use of a pre-atomization system which further improves the ability to provide minute droplet size. The device according to this invention further employs a single moving part and can be machined using conventional processes.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.